Arkansas has 38 death row prisoners, and has executed 27 since the death penalty restarted in 1976.

A drug manufacturer based in Britain has vowed to add new restrictions to sales of its products in the US after it was revealed that it sold a batch of barbiturate to the Arkansas department of corrections, which intended to use it in executions.

Hikma Pharmaceuticals has promised to put in place "concrete steps to restrict the supply of its products for unintended uses" following the disclosure by the legal action charity Reprieve that a wholly owned subsidiary in the US had sold injectable phenobarbital to the Arkansas prison service which was seeking to devise a new way of killing its death-row inmates.

"Hikma strongly objects to the use of any of its products in capital punishment," the company said in a statement.

Hikma is the latest pharmaceutical company to be caught selling death penalty drugs to the US amid a growing boycott across Europe and around the world of lethal injection drug sales to capital punishment states. It follows a line of firms, including the Danish company Lundbeck and the US manufacturer Hospira, to place legal or production hurdles in the way of such sales.

Ironically, Arkansas turned to the Hikma subsidiary, West-Ward Pharmaceuticals in Memphis, Tennessee, as a possible way of skirting the drug boycott. Since 2011 execution drugs have been in increasingly short supply after the European commission banned exports of listed chemicals to all US corrections departments.

With other options closed down, Arkansas decided to pioneer a new death penalty protocol untested by any other state: the use of phenobarbital, a barbiturate widely used medically as an anticonvulsant. This year the state adopted a new protocol that involves executing prisoners by injecting them with a relaxant, Lorazepam, followed by 12 grams of phenobarbital hydrochloride.

In April, West-Ward Pharmaceuticals shipped two batches of Phenobarbital to Arkansas department of corrections in Pine Bluff amounting to a total of almost 100 grams of the chemical – sufficient to kill eight prisoners. A spokesman for Hikma said the order had been made as part of the regular automated request for drugs for the general prison hospital services and given that phenobarbital has never been used in executions before in the US, it raised no red flags with the company.

Hikma added that the quantity of the drug was small, though a spokeswoman for the Arkansas department of corrections said it was "enough to perform several executions".

Maya Foa, a death penalty expert with Reprieve, welcomed Hikma's pledge to cut off the supply route to US corrections departments in capital punishment states. "This shows that the pharmaceutical industry is not willing to have its products used in executions. The industry now understands that it can stop its drugs reaching death chambers."

Arkansas confirmed to the Guardian that it had been contacted by West-Ward and told that it was closing the account. That presents the state with a long-term problem, but in the short term it still has plenty of phenobarbital with a shelf life that will last until October 2015.

Arkansas has 38 death row prisoners, and has executed 27 since the death penalty restarted in 1976. There are no executions scheduled this year, though in anticipation of a warrant being issued, six death row inmates have challenged the use of phenobarbital potentially to kill them through the courts.

In their complaint, the condemned men say that Arkansas has chosen "a completely untried combination and quantity of drugs that will take hours to be injected and to reach their peak effect, that will produce agonising and degrading effects during the procedure, and that will severely and permanently injure – but may not kill – the prisoners".

• The headline on this article was amended on 17 May 2013 to reflect the story more clearly. The original headline was "British maker of death penalty drugs adds new restrictions for US buyers".